Microhematocrit tube



1963 M. A. ASNES ETAL 3,

MICROHEMATOCRIT TUBE Original Filed Oct. 21, 1965 m i Z F IG. 4

INVENTOR.

mxww A TT FM L United States Patent 3,416,361 MICROHEMATOCRIT TUBE Marvin A. Asnes, New. York, and Richard K. Bernstein, Bronx, N.Y., assignors to Clay-Adams, Inc., New York, N.Y., a corporation of New York Continuation of application Ser. No. 499,579, Oct. 21, 1965, which is a continuation-in-part of application Ser. No. 174,185, Feb. 19, 1962. This application June 23, 1966, Ser. No. 562,425

2 Claims. (Cl. 73-61) ABSTRACT OF THE DISCLOSURE A calibrated micro'hematocrit tube for making microhematocrit determinations using a reader having a linear scale, and a method of using such a tube.

This application is a continuation of application Ser. No. 499,579, filed Oct. 21, 1965, now abandoned, which is a continuation-in-part of application Ser. No. 174,185 filed Feb. 19, 1962, now bandoned.

By standard procedures, the patients finger is punctured and squeezed to provide a large drop of blood. A uniform bore capillary tube is disposed with one end thereof within the drop of blood and the tube is tilted downwardly so that the capillary action is aided by gravity in filling the tube. If the tube is insufficiently filled, a second drop of blood is squeezed from the finger. This may have to be repeated several times before the tube is adequately filled. However, excess squeezing pressure must be avoided to prevent the exuded blood drop from including tissue fluid which adversely affects the determination.

The filled tube is sealed at one end by one of several alternative procedures. In one case, the tube is turned vertically to bring the still dry end thereof in a lowermost position and the same is inserted into soft plastic clay to seal the same. The clay is commonly carried in a tray which permits the filled tubes to be left upstanding therein for storage and transportation.

Thereafter, the filled sealed tube is placed on the head of a centrifuge with the sealed end extending outwardly and the blood sample is spun down by the centrifuge operating at a predetermined speed and for a set time interval. The blood sample will now be stratified as between the red cells and the plasma. The hematocrit is determined as the percentage of the red cell column length of the total column length of the sample.

Readers are provided for such determinations; the same having spiral or other special forms of percentage scales. The centrifuged tube is located on the scale and must be moved relative thereto so as to first register the lower end of the sample column with the 0% marking of the scale. Then the tube is further moved to register the upper end of the sample column with the appropriate portion of the 100% marking of the spiral or other scale. These two necessary movements are at right angles to each other and necessarily affect the time interval for making each determination and may also affect the accuracy of such determinations.

Accordingly, one object of thisv invention is to provide a microhematocrit tube which is precalibrated by a suitable marking at a given point in the length thereof, to provide uniform blood samples of a given volume and column length. With such tubes, a reader having uniform graduations and a scale calibrated to the specific column length of the tubes, may be used. With such a reader and tubes, the second movement described above is eliminated and the single movement of the tube to register 3,416,361 Patented Dec. 17, 1968 the lower end of the sample column with the 0% marking allows for an immediate determination.

Conventional microhematocrit tubes are formed of glass tubing having a bore of the order of 0.83-1.04 mm., with an average bore of about 0.97 mm., for tubes of the usual mm. length. For the shorter 32 mm. tubes the bore is of the order of 0.63-0.75 mm., with an average of about 0.69 mm. Recently, it has been proposed to enlarge the bore of the 75 mm. tubes to 1.07-1.24 mm. with an average of 1.15 mm. The Wall thickness of the 75 mm. tubes is about 0.20-0.22 mm. and of the 32 mm. tubes, about 0.31 mm.

With conventional 75 mm. tubes, the usual blood sample carried in such tubes may have a volume of the order of 44.0 to 62.5 cu. mm. Preferably, the column length of the sample should be at a maximum to assure reasonable accuracy in the percentage determination. However, with the conventional 75 mm. tube it is difficult to obtain sutficient blood to fill more than 50-60% of the tube length, without resort to excessive squeezing of the patients finger and incident contamination by tissue fluid.

Also, with such conventional tubes, the movement of the tube to its vertical, sealing position, normally results in a rapid gravitational How of blood to the lower end thereof, thus wetting the inner tube surface at that end to an extent which impairs the clay seal. With such imperfections in the clay seal, blood leakage during the centrifuging operation is not unusual. In lieu of clay seals, the tubes have been flame sealed but such seals are inconvenient to produce, slow down the rate of determinations, make short sample columns mandatory, and may adversely affect the blood sample due to heat transmitted thereto with resultant hemolysis of the blood.

Thus, another object of this invention is to provide an improved microhematocrit tube which has a relatively narrow bore so as to allow for a blood sample of maximized column length of about 60 mm. in a 75 mm. tube, to insure maximum accuracy in readings; which permits inversion of the tube to its vertical position without loss of blood or wetting of the inner surface thereof at the dry end thereof, thereby assuring optimum clay seals free of leakage; and a tube wall thickness which substantially reduces tube breakage.

Still another object of this invention is to provide an improved microhematocrit tube which has a minimized lbore diameter to allow a blood sample of extended column length to be carried therein for optimum accuracy in readings, yet allowing the capillary forces of such tube bore to retard the flow of blood on manipulation of the tube during sealing so as to avoid wetting the inner surface of the initially dry end of the tube which is to be sealed.

Yet another object of this invention is to provide an improved microhematocrit tube which is calibrated to allow for filling the same with a blood sample of predetermined maximum length, yet minimized volume, whereby the tube filling time is materially reduced, trauma to the patient is minimized because of the smaller blood requirement, and which permits the usage of simplified reader scales therewith.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

In the drawing, FIG. 1 is a plan view of a microhematocrit tube embodying the invention;

FIG. 2 is a transverse section thereof taken on the line 2.2 of FIG. 1;

FIG. 3 is a partial elevational view showing the tube in its sealing position; and

FIG. 4 is a plan view of the tube in position on a reader.

As shown FIGS. 1 and 2, the microhematocrit tube 10 embodying the invention is formed of glass tubing cut to selected lengths, preferably 75 to 85 mm. for the usual long tubes, or 30 to 40 mm. for the shorter tubes. The opposite ends 11, 12 of the tubes are fire polished in the usual manner.

Tube has a bore 13 of a selected diameter ranging from about 0.50 to 0.60 mm., and preferably 0.55 mm. in diameter. The thickness of tubing wall 14 is about 0.38 to 0.65 mm.; the aforesaid bore and wall thickness dimensions providing unique characteristics for such microhematocrit tubes, as hereinafter described.

The tube 10 is provided with a calibration marking 15 which is measured to a point 60 mm. from tube end 11, in a 75 mm. tube. Marking 15 will not rub off in normal use and extends completely around the tube, with a width of the order of 0.5 mm. to provide for clear reading. The bore diameter is uniform throughout the length of the tube and provides a volume of about 15.0 cu. mm. for the 60 mm. length.

In using the microhematocrit tube 10 of the instant invention, the tube end 11 is inserted into the blood drop and the tube held in a level position to draw blood by capillary action to a distance about half way to marking 15. On tilting tube 10- downwardly somewhat, blood will flow therein toward the marking 15. The blood fiow is readily controlled by suitable tilt of the tube 10, upwardly to reduce or stop the blood flow, and downwardly to increase the same. When the tube 10 has been filled to marking 15, the tube is removed from the patients finger.

At this time, tube 10 is ready for sealing, as by the use of soft plastic clay 16 carried in a tray 17. The blood filled tube 10 is turned to a vertical position with the dry end 12 thereof in a lowermost position and said end is inserted into clay 16 to provide a plug 18 within the tube end. While the blood in tube 10 will tend to flow toward end 12, such flow is at a very slow rate, which permits the plug 18 to be formed before the inner surface of tube end 12 has become wet with blood. The plug 18 will vary in length, and is usually of the order of 2 to 5 mm. in length.

As the clay plug 18 is formed on a dry glass surface at tube end 12, the resultant seal will be tight and resistant to blood leakage. The sealed tubes 10 are left upstanding on tray 17, which is used as a carrier therefor, until all the tubes 10 are in a sealed condition and are ready to be centrifuged. It will be apparent that tubes 10 having been filled to calibration mark 15, each tube will then carry a uniform volume of blood sample and with a uniform column length.

The filled tubes 10 are now centrifuged in the usual manner to effect Stratification of the samples therein, providing red cells and plasma is serial relation. The centrifuged tubes are now ready for reading and a reader 20 is provided for the purpose. Reader 20, as shown in FIG. 4, has a scale of uniformly spaced graduations over a length of 60 mm. corresponding to the 60 mm. length of the original blood sample in tubes 10. The tube 10 is located on the reader 20 with the lower end of the sample column therein corresponding to the top 21 of plug 18, registered with the 0% marking of scale 22 on said reader.

The demarcation point corresponding to the stratification of the red cells and plasma in tube 10, indicated at 23 may now be read directly as a percentage on scale 22, without further manipulation of tube 10. Thus, a percentage reading may be obtained with a single movement of tube 10 relative to reader 20, thus increasing the rate of determinations.

While reader 20 may be separate and apart from the centrifuge used to effect stratification of the blood samples in tubes 10; such reader is particularly adapted to be incorporated within the centrifuge, the reader scale markings being engraved or otherwise formed directly on the centrifuge head surface over which the tubes 10 he during the centrifuging action. Thus, the tubes 10 would not have to be removed from the centrifuge to obtain readings.

Although, tubes 10 have been disclosed to have calibration markings at 60 mm. for the 75 mm. tubes, it is understood that with minimized bore diameters other maximized column lengths may be used, with linear reader scales correspondingly adjusted. However, the column length is preferred at a minimum of about 50 mm. and a maximum length which still leaves tube 10 with an unfilled portion of at least 10 mm. in length.

It has been found that tubes 10 with their markedly reduced bore diameters and sample volumes, are rapidly filled with a minimized quantity of blood from the patient, thus avoiding undue trauma and contamination of the sample by tissue fluid. Also, the flow of blood within the tubes upon inversion thereof for scaling, is retarded to an extent that permits sealing before the dry ends of the tubes can be wet by the fiow of blood, which facilitates the use of clay seals and avoids leakage. Further, with a minimum bore diameter not less than 0.50 mm., the blood column in tubes 10 is readily perceptible to the human eye, thereby facilitating readings and insuring greater accuracy in such readings.

Also the novel tubes of the instant invention have a wall thickness larger than that of conventional tubes, despite a slightly smaller outside diameter. Such increase in wall thickness accruing from the decrease in bore diameter, has produced a marked reduction in breakage of tubes.

In the case of tubes of shorter lengths, the calibration mark is located so as to provide a sample column length of about of the total length of the tube. It is understood that readers will have linear scales which correspond to the calibrated column length of the tubes to be used with such readers; all scales being uniformly subdivided for the standardized column length thereof. Since the tubes of the instant invention can be read with minimized manipulation, the linear reader scales can be located directly on the centrifuge head to thereby obtain a reading without removing the centrifuged tubes from the head.

As various changes might be made in the embodiment of the invention herein disclosed without departing from the spirit thereof, it is understood that all matter herein shown or described shall be deemed illustrative and not limiting except as set forth in the appended claims.

What is claimed is:

1. A method of making a microhematocrit determination from a centrifuged stratified blood sample contained in a microhematocrit tube, said tube having a length of about 75 mm. and a uniform bore diameter throughout the length thereof from about 0.50 to about 0.60 mm. with the minimum bore diameter being such that the blood column therein is readily perceptible to the human eye, said tube having a single calibration marking thereon located adjacent one end of said tube and at a point of about 60 mm. from the other end thereof to provide a predetermined tube length from said marking to said other end of said tube and a volumetric capacity over said tube length of about 15.0 cubic mm., filling the bore of said tube with the blood sample, allowing the blood sample to move slowly toward said one end of said tube by invert-ing the tube to bring said one end thereof to the lowermost position thereby allowing for sealing of the bore surface at said one end of the tube with plastic clay before said bore surface is wet by the slowly moving blood sample, said filling procedure being continued until the bore of the tube is filled to the single calibration marking so that said blood sample is of a continuous longitudinal length equal to said predetermined distance, sealing said tube at said one end thereof, subjecting the blood sample to centrifugal forces to fractionate the blood, disposing said sample containing tube along a linear percentage scale reader graduated uniformly from zero percent to over a distance equal to said predetermined distance with the one end of the sample in said tube adjacent to the sealed end thereof in alignment with the zero percent marking on said reader whereby the demarcation point between adjacent strata of the sample in the tube may be read directly as a percentage on said scale reader without further movement of said tube relative to said reader.

2. A method of making a microhematocrit determination from a centrifuged stratified blood sample contained in a microhematocrit tube, said tube having a length of about 60 to 85 mm. and a uniform bore diameter throughout the length thereof of from about 0.50 to about 0.60 mm. with the minimum bore diameter being such that the blood column therein is readily perceptible to the human eye, said wall thickness being from about 0.38 to about 0.65 mm., said tube having a single calibration marking at a point not less than about 10 mm. from one end thereof and at least about 50 mm. from the other end thereof to provide a predetermined tube length from said marking to said other end of said tube, filling the bore of said tube with the blood sample, allowing the blood sample to move slowly toward said one end of said tube by inverting the tube to bring said one end thereof to the lowermost position thereby allowing for sealing of the bore surface at said one end of the tube with plastic clay before said bo-re surface is Wet by the slowly moving blood sample, said filling procedure being continued until the bore of the tube is filled to the single calibration marking so that said blood sample is of a continuous longitudinal length equal to said predetermined distance, sealing said tube at said one end thereof, subjecting the blood sample to centrifugal forces References Cited FOREIGN PATENTS 3/1955 Great Britain.

OTHER REFERENCES Miller, Textbook in Clinical Pathology, 6th ed., The Williams and Wilkins Co., Baltimore, Md., 1960, pp. 38-46.

Kimble Laboratory Glassware, Catalog SP75, November 1961, pp. 250, 262, 266.

S. CLEMENT SWISHER, Acting Primary Examiner.

W. A. HENRY II, Assistant Examiner. 

